Method for adding tellurium dioxide to molten steel

ABSTRACT

ADDING TELLLURIUM TO MOLTEN STEEL USING BRIQUET CONTAINING COMPACTED TELLURIUM DIOXIDE POWDER AND STEEL MACHINE SHOP TURNINGS.

United States Patent 3,574,606 METHOD FOR ADDING TELLURIUM DIOXIDE T0 MOLTEN STEEL William Edgar, Glenwood, Ill., and Ralph E. Pray, Pasadena, Calif., assignors to Inland Steel Company, Chicago, Ill. N0 Drawing. Filed July 3, 1968, Ser. No. 742,167 Int. Cl. C22c 33/02, 39/54 U.S. Cl. 75-129 5 Claims ABSTRACT OF THE DISCLOSURE Adding tellurium to molten steel using briquet containing compacted tellurium dioxide powder and steel machine shop turnings.

BACKGROUND OF THE INVENTION 3,574,606 Patented Apr. 13, 1971 ICC of tellurium dioxide plus lead and approached that recovery obtained with elemental tellurium.

As used herein, the term turnings includes shavings, grindings, borings, chips and the like.

Adding a briquet of tellurium dioxide plus turnings to the ingto mold immedediately after cushioning provides a better recovery than that obtained when the briquet is added to an empty mold. Cushioning refers to a procedure in which the bottom portion of an empty ingot mold is slowly filled with molten steel until about 5%, for example, of the ingot mold contains molten steel. Thereafter, the molten steel is added to the ingot mold at a substantially increased rate.

A ratio of turnings to tellurium dioxide of about 3:1 gives a better recovery of tellurium than do other ratios, both lower and higher.

A binder is not required to hold the briquet together; a reducing agent incorporated into the briquet has no significant effect upon the recovery of the tellurium; and fiuxes are not needed in the briquet.

Other features and advantages are inherent in the method and product claimed and disclosed or will become apparent to those skilled in the art from the following detailed description.

DETAILED DESCRIPTION OF THE INVENTION INCLUDING PREFERRED EMBODIMENTS The relative recovery of tellurium from briquets composed of tellurium dioxide alone, tellurium dioxide plus lead, and tellurium dioxide plus turnings is reflected in the following Table I.

available tellurium dioxide is in the form of a fine powder. When tellurium dioxide is added to steel as finely divided powder, recovery is poor and there are undesirable tellurium fumes in excessive amounts.

Compacting the finely divided tellurium dioxide powder into briquets improves the recovery and decreases the fumes, but the resulting recovery is still too poor to compete commercially, with the addition of tellurium in elemental form. The tellurium dioxide briquet floats on the surface of the molten steel in the ingot mold; and the relatively poor recovery was initially wholly attributed to the failure to get the tellurium dioxide below the surface of the molten metal. To get the briquets below the surface requires briquets of increased density.

Tellurium and lead are often added together to steel to improve the machinability thereof; and one way to increase the density of the briquets is to combine the tellurium dioxide and lead, in the form of shot (about 20 mesh), in one briquet. However, although these briquets are sufficiently dense to sink below the surface of the molten metal to the bottom of the ingot mold, the recovery of tellurium thus obtained is no better than that obtained using briquets of tellurium dioxide without lead.

SUMMARY OF THE INVENTION Despite the poor recovery obtained with relatively dense briquets composed of tellurium dioxide plus lead, when the tellurium dioxide was briqueted with steel ma chine shop turnings and the resultant briquet was added to the ingot mold, the recovery of tellurium thus obtained was significantly higher than that obtained with briquets Table I shows that from the standpoint of tellurium recovery there is no difference between briquets composed of tellurium dioxide alone (Ingot A) and briquets composed of tellurium dioxide plus lead (Ingots C and D); whereas, there is a substantially improvement for briquets composed of tellurium dioxide plus turnings (Ingot E). The addition of a reducing agent (lamp black or pitch) had no significant effect upon tellurium recovery. (Compare Ingot A with Ingot B and Ingot C with Ingot D.)

The following Table II reflects the relative tellurium recoveries for various ratios of turnings to tellurium dioxide in a briquet. All the additions reflected in Table II were made to the ingot mold after cushioning Table II shows that a ratio of turnings to tellurium dioxide of 3:1 (Ingots I, J and K) is better than either 2:1 (ingots F, G and H) or 4:1 (ingots L and M) and produces a tellurium recovery essentially the same as that obtained with elemental tellurium (Ingot N).

It is desirable that the total weight of briquets added to the steel to give the desired tellurium content be as low as possible. A briquet having a ratio of turnings to tellurium dioxide of 3:1 is, of course, of less weight than a briquet having a higher ratio.

Thus, a weight ratio of turnings to tellurium dioxide in the briquet of about 3:1 is preferred, but a ratio of between 2:1 and 5:1 is permissible.

The following Table III shows the compartive tellurium recovery obtained when adding the briquets to an empty ingot mold and to an ingot mold immediately after cushioning. A ratio of turnings to tellurium dioxide of 3:1

was used in each case where a briquet was added.

TABLE III Tellurium dioxide is normally available commercially as a finely divided powder, 80% of which has a particle size greater than 100 mesh.

A typical briquet is about a two inch cube and has a density of five to six grams per cubic centimeter. The briquet should have a mass sufiicient to break through the surface tension of the molten steel in the ingot mold which has undergone cushioning. If the briquet is too small, there is a relatively rapid breakdown of the briquet into its components; and the breakdown is too rapid for satisfactory recovery of tellurium. The maximum size of the briquet is determined by the cross-sectional size of the ingot mold, by convenience of briqueting and by the capabilities of the equipment used to handle the briquets.

Composition of addition Method of addition Te recovery, percent TeOz+turnings Empty ingot mold..-

do -do Table III shows that, when the addition is made after cushioning (Ingots U through Y), recovery of tellurium is better than when addition is made to an empty ingot mold (Ingots 0 through S).

Adding the briquet to the ingot mold after cushioning, rather than placing it in the empty ingot mold, not only improves the tellurium recovery but also minimizes the possible loss of tellurium if a leak develops in the ingot mold when the molten steel is initially introduced thereinto. If a leak develops during cushioning and before the tellurium is added, a loss of tellurium is avoided; but, on the other hand, if the tellurium is placed in an empty ingot mold and a leak develops upon the initial addition of molten steel, the loss of tellurium cannot be avoided. Avoiding losses of tellurium is especially important because of the relatively high cost of tellurium, e.g., $6.00 a pound or higher.

Adding the briquets as soon after cushioning as possible facilitates distribution of tellurium in the ingot. The sooner the briquet is added, the more even the distribution.

From the standpoint of machinability, there is no substantial diflerence in ma-chinability between steel bars having tellurium added as tellurium dioxide, in briquets containing tellurium dioxide plus turnings, and steel bars having tellurium added in elemental form. On the other hand, the machinability of steel bars containing tellurium added as briquets of tellurium dioxide alone or tellurium dioxide plus lead was not great enough to compete commercially with bars containing tellurium added in elemental form.

The best machinability corresponded to the best tellurium recovery. In other words, a bar produced from an ingot to which tellurium dioxide is added, in briquets containing tellurium dioxide plus turnings, with a ratio of turnings to tellurium dioxide of 3:1 and with the briquet being added immediately after cushioning, has the best machinability.

The procedures and techniques described above for adding tellurium to steel in the form of tellurium dioxide may also be used to add selenium to steel in the form of selenium dioxide. Selenium, like tellurium, is added to steel to improve the machinability thereof.

The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood thereform as modifications will be obvious to those skilled in the art.

We claim:

1. A method for adding, to steel, tellurium in the form of tellurium dioxide, said method comprising the steps of:

providing a briquet consisting essentially of tellurium dioxide powder and steel turnings;

and adding said briquet to an ingot mold incident to the teeming of the ingot.

2. A method as recited in claim 1 wherein the ratio of steel turnings to tellurium dioxide in said briquet is in the range of 2:1 to 5:1.

3. A method as recited in claim 2 wherein the ratio of steel turnings to tellurium dioxide is 3: 1.

4. A method as recited in claim 1 and comprising:

cushioning said ingot mold;

and adding said briquet to said ingot mold after said cushioning.

5. A method as recited in claim 4 wherein the briquet is added to the ingot mold immediately after said cushioning.

References Cited UNITED STATES PATENTS 2,25 3,502 8/ 1941 Boegehold -l23 2,364,922 12/ 1944- Smalley 75123X 2,563,056 8/ 1951 Miller 75-53 .L. 'DEWAYNE RUTLEDGE, Primary Examiner J. E. LEGRU, Assistant Examiner U.S. Cl. X.R. 75-.5, 53, 123AA 2 3 3 IJNITED STATES PATENT OFFICE CERTIFICATE -OF CORRECTION Patent No. 3,574,606 Dated April 13, 1971 Inventor) William Edgar and Ralph E. Pray It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2 line 6, delete "ingto" and insert ingot Column 2 line 45 delete "substantially" and insert --substan Column 2 under heading "Te recovery percent" line 62, delete 66.7" and insert --66.O-; line 63, delete "75.8" and insert 75.7; line 64, delete "70 2" and insert --70 8-- line 65, delete "6 9 8" and insert -69 2- line 66 dele'te "62 0" and insert -62 8 Signed and sealed this 17th day of August 1971 (SEAL) Attest:

EDWARD I'LFLETCHERJR. WILLIAM E. SCHUYER, J1

Attesting Officer Commissioner of Patent 

